1. Field of the Invention
The present invention relates to a payload pointer processing system responsive to a synchronous payload envelope in a digital data transmission network, and more particularly to a system in which a plurality of payloads are lumped together to form an appropriate number of group units and pointer processing is effected by every group unit and a shared control of storage in a pointer processing device leads to a reduction of multiconversion units to curtail the scale of a pointer processing circuit.
2. Description of the Related Arts
In an internationally standardized synchronous optical transmission device such as by CCITT (Comite Consultatif International Telegraphique et Telephonique) and SONET (Synchronous Optical Network), it is requested for the above-described device that a synchronous payload envelope be used to be regarded as a transmission unit to transmit information, and the assignment of a timely location or a time slot, with regard to a plurality of synchronous payload envelopes, is carried out to multiplex therewith. In the payload pointer processing system in response to such a synchronous payload envelope it is requested that the processing system be constituted such that the scale of the pointer processing circuit can be reduced.
As for the payload pointer, in internationally standardized synchronous optical transmission equipment, it is recommended by the international standard to be capable of efficiently processing the payload envelope with regard to time and hardware.
When a plurality of payload envelopes such that a frame phase is not mutually defined is byte-multiplexed, the payload pointer is defined in a superframe structure for transmitting a payload envelope. That is, the frame structure in this case is formed by the payload envelope as well as a surplus byte (overhead byte) that includes the payload pointer value, or the like, that shows where the head position of the payload envelope is present in the designated frame structure or mapping, viz., an overhead byte (for example, in the case of a VT superframe, it is regarded as V1 to V4).
Since a circuit for performing a pointer processing is necessitated by a number of the payloads, when a large number of payloads are converted in a multi-fold way or in the case of a transmission device that new inserted payloads and a group of received payloads are combined and assigned again, it is necessary to prepare a great number of pointer processing circuits and it is inevitable that the scale of the circuit be increased. Further, even in a transmission device that is applied to a synchronized network, since a fluctuation such as a wander or jitter exists, it is quite difficult to carry out a payload pointer processing and realize a multiplexer or a relocation equipment.